The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Engines such as diesel engines produce particulate matter (PM) that is filtered from exhaust gas by a PM filter. The PM filter is disposed in an exhaust system of the engine. The PM filter reduces emission of PM that is generated during combustion.
Over time, the PM filter becomes full. During regeneration, the PM may be burned within the PM filter. Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy. The resistive heating coils are typically arranged in contact with the PM filter to allow heating by both conduction and convection.
Regeneration may be performed using an exhaust heating technique or using an electrical heating technique. An exhaust heating technique refers to the heating of an exhaust gas, for example, by post injection of fuel. During a combustion cycle of an engine, an air/fuel mixture is compressed and ignited within a cylinder of the engine. To facilitate regeneration, fuel may be injected into the cylinder during the combustion cycle and after ignition of the air/fuel mixture or into the exhaust stream. When introduced during or after ignition and/or exhaust strokes of the combustion cycle, the injected fuel, referred to as post-injected (PI) fuel, mixes with the exhaust gas and is oxidized by an oxidation catalyst disposed in the exhaust system. The heat released from the oxidation reaction in the catalyst increases the temperature of the exhaust system, which facilitates the ignition of the particulates in the PM filter.
The electrical heating technique refers to the electrical heating of an exhaust gas entering a PM filter. One or more electrical coils may be disposed upstream from the PM filter and may be activated to heat the exhaust gas. This provides a quick heating and light off of the PM.
PM reduction systems that use fuel tend to decrease fuel economy. For example, many fuel-based PM reduction systems decrease fuel economy by 5%. Electrically heated PM reduction systems reduce fuel economy by a negligible amount, but are operation-limited based on exhaust flow. As exhaust flow increases, for example, above a particular flow rate (kg/s), the facilitation and ability to initiate regeneration by an electrically heated element decreases.